Troat plates are easily replaced (even with correct part number). It's not that easy to find one in perfect condition, but for some models there are brand new available. Refurbishing an original case is perhaps the best (no need to scavange another machine), but original cases turn up, even identical. An all original machine in superb condition is always a pluss and something a bit out of the ordinary, but a well restored machine is very nice too. Unless it's something very special the money value is not great either way. A newly rewired and service machine will always fetch a good price, but still it's nothing close to a brand new modern top model.